For several decades, the issue of protecting the occupants of a military or civilian vehicle subjected to an explosive detonation has become a major concern for decision-makers, both during peacekeeping operations and armed conflicts. Several technical solutions have been considered, and some have been implemented. These solutions are essentially based on energy dissipation through material deformation.
For example, document GB 2,452,589 A describes such an energy absorption device that is intended to protect occupants from the effects of an excessive G-force. The device comprises a mitigating strip positioned between a chassis of the vehicle and a structure attached to the occupant's seat. During an explosion, the mitigating strip is bent and pulled between rollers that are secured to the structure of the occupant's seat, which makes it possible to absorb part of the energy.
A shock absorption device provided with a platform supporting a load to be protected from a shock is known from document U.S. Pat. No. 3,446,469. The platform is mounted on a scissor mechanism with compressible units positioned below the platform and intended to deform in case of shock.
Documents SU 431,066, EP 1,155,940, U.S. Pat. No. 3,696,891, U.S. Pat. No. 4,509,621 and FR 2,085,498 teach energy absorption devices comprising a dissipating element deformed using balls.
In general, the mechanisms proposed in the prior art are designed to dissipate a maximum amount of energy over a given travel, but sized so that the response of the shock absorber is optimized for a given configuration of the threat, i.e., characteristics of the explosion (explosive charge, distance between the explosive and the vehicle, etc.) assumed beforehand.
Furthermore, the proposed mechanisms generally do not make it possible to control the plastic deformations involved. As a result, the acceleration experienced by the occupant during the shock varies over time with a peak at the beginning of travel followed by a decrease until all of the energy involved has been dissipated.
Moreover, proposed mine protection mechanisms are designed so as to offset the blast of an explosion occurring under a vehicle, i.e., to offset the initial shock experienced by the occupants when the vehicle is projected upward. In general, these mechanisms do not take into account the second shock, called the “drop-down”, caused when the vehicle returns to the ground. Yet the acceleration experienced during the secondary shock, although having a lower amplitude than the primary shock, is nevertheless very significant and has the characteristic of being felt over a longer time interval than the first shock.
Document WO 2010/105055 provides part of the solution to the various problems described above. The energy dissipation device proposed in that document is mechanical or hydraulic and comprises means for adjusting the degree of absorption based on the weight of the occupant, for both the primary and secondary shocks. The system provides an adjustment that may be different for the primary shock and the secondary shock, and which can therefore be optimized to take into account the different characteristics of the two shocks in terms of acceleration. However, this device has the drawback that the system is repositioned in the rest position or, in other words, reset between the primary shock and the secondary shock. Taking the different characteristics of the two shocks into account will therefore require a real-time adjustment between the two shocks. In the field, it is unlikely that such a system will be operational, since the first shock causes considerable mechanical and electronic damage that will make the real-time adjustment before the second shock difficult, or even impossible.